The invention relates to a method and apparatus for operating high-temperature fuel cells with ion-conducting electrolyte wherein hydrogen and oxygen-containing ions are converted to water with the production of electrical power, and with oxygen in the form of an oxygen-containing gas being supplied to the cathode of the fuel cell.
German Application P 38 10 113 discloses a process for operating fuel cell systems. The feedstock therein is a fuel gas, for example a gas from a partial oxidation, town gas, or natural gas which is converted, in a synthesis gas generator with the addition of steam, into an H.sub.2 /CO synthesis gas. This synthesis gas is subjected to a CO conversion, and the thus-formed H.sub.2 fuel gas is fed to the anode side of the fuel cell.
The cathode is supplied with a mixture of carbon dioxide and air. During this process, CO.sub.3.sup.2- ions are formed from oxygen and carbon dioxide at the cathode; these ions diffuse through the ion-conducting electrolyte and are converted to water and carbon dioxide at the anode with hydrogen. It has been found that the nitrogen in the air passed into the cathode covers parts of the cathode due to polarization. This results in a decrease in the conversion of CO.sub.2 and O.sub.2 to CO.sub.3.sup.2- ions and a concomitant reduction in the efficiency of the cell. In addition, from the cathode, an outlet gas is generally withdrawn containing unreacted components and inert components, a portion of which is returned to the cathode after cooling, compression and reheating, in order to regulate the temperature of the fuel cell. When using a CO.sub.2 -air mixture, an outlet gas primarily containing nitrogen will then be obtained at the cathode, and owing to the recycling procedure, this gas dilutes the effective oxygen and carbon dioxide proportions supplied to the cathode side, the dilution being evident even at the inlet to the cathode. Finally, the required removal of the nitrogen results in a large waste gas stream, and CO.sub.2 valuable for the process is, perforce, lost with this waste gas stream.